Electric engines comprise rotors with high revolution speeds, enclosed by stators typically cooled by fans connected to or driven by the shaft of the rotor.
Part of the rotational energy of the rotor is expended accelerating air passed across the rotor. A certain amount of air needs to pass the rotor in order to keep it cool, however, any excess results in unnecessary energy expenditure, reducing the overall energy efficiency of the engine.
In an arrangement for an electric engine, fans are located at either end of the rotor blowing cooling air axially across the rotor from both ends. The convergence of the cooling air subsequently forces it radially through cooling slots in the stator. In another arrangement a single fan is used where cooling air is either blown or sucked across the rotor from where a component of the cooling air flows radially from the rotor through to the stator. In both these arrangements cooling air in excess of what is required to cool the rotor initially passes over the rotor resulting in lower engine energy efficiency.
DE 39 05 997 discloses another arrangement for cooling the coils of an induction motor. The arrangement includes a closed and smooth cylinder jacket attached to, in one induction motor arrangement, stator coil formers and, in another induction motor arrangement, rotor coil formers. In each alternative form the jacket provides the coil of the induction motor with a cooling channel in which a fan can exclusively provide cooling of the coils. U.S. Pat. No. 4,347,451 discloses a further cooling arrangement applied to a salient pole dynamoelectric machine. In the arrangement a barrier enables separate cooling of the stator and rotor by means of forced draft supplied from respective exclusive blowers.